System Attacks Disrupting User’s Access

If you’re planning on taking the Security+ exam, you should have a basic understanding of several common types of attacks launched against systems and networks such as system attacks that disrupt users from accessing services.

For example, can you answer this question?

Q. An IDS alerts on increased traffic. Upon investigation, you realize it is due to a spike in network traffic from several sources. Assuming this is malicious, what is the MOST likely explanation?

Random 100-question tests

Random practice tests from the all of the practice test questions in the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide. All questions include explanations so you'll know why the correct answers are correct, and why the incorrect answers are incorrect.

34 Simulated Performance-based Questions

Eight sets of performance-based questions with multiple questions in each set. These questions help you understand and prepare for performance based questions.

22 Realistic Performance-based Questions

Two new sets of performance-based questions with a total of 22 questions. These new questions use a new testing engine that includes realistic drag and drop, matching, sorting, and fill in the blank questions.

Flashcard Set

273 Security+ Flashcards to reinforce key testable concepts

280 Security+ acronyms flashcards to help you master the required acronyms

204 Security+ Remember This slides

Audio - SY0-401 Security+ Remember This Audio Files

Learn by Listening. Over one hour and 15 minutes of audio (MP3 downloads.)

Audio - SY0-401 Security+ Question and Answer Audio Files

Learn by Listening. Over three hours hour and 15 minutes of audio (MP3 downloads.)

Bonus #1

Audio from the end of chapter reviews from each of the chapters in the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide. Over one hour and 15 minutes of additional audio.

Bonus #2

Subnetting mini-tutorial that will help you answer two key question types:

Identify how many hosts a subnet supports

Identify valid IP addresses within a subnet

Bonus #3

Access the study materials for a total of 60 days because sometimes life happens.

DoS Versus DDoS

A denial-of-service (DoS) attack is an attack from one attacker against one target. A distributed denial-of-service (DDoS) attack is an attack from two or more computers against a single target. DDoS attacks often include sustained, abnormally high network traffic on the network interface card of the attacked computer. Other system resource usage (such as the processor and memory usage) will also be abnormally high. The goal of both is to prevent legitimate users from accessing services on the target computer.

Many DoS and DDoS attacks attempt to consume resources on the target computer. For example, a SYN (synchronize) flood attack consumes memory resources by flooding a system with half-open connections.

Remember this

A denial-of-service (DoS) attack is an attack from a single source that attempts to disrupt the services provided by another system. A distributed denial-of-service (DDoS) attack includes multiple computers attacking a single target. DDoS attacks typically include sustained, abnormally high network traffic.

SYN Flood Attacks

The SYN flood attack is a common attack used against servers on the Internet. They are easy for attackers to launch, difficult to stop, and can cause significant problems. The SYN flood attack disrupts the TCP handshake process and can prevent legitimate clients from connecting.

Chapter 3 of the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide, “Understanding Basic Network Security,” explained how TCP sessions use a three-way handshake when establishing a session. As a reminder, two systems normally start a TCP session by exchanging three packets in a TCP handshake. For example, when a client establishes a session with a server, it takes the following steps:

The client sends a SYN (synchronize) packet to the server.

The server responds with a SYN/ACK (synchronize/acknowledge) packet.

The client completes the handshake by sending an ACK (acknowledge) packet. After establishing the session, the two systems exchange data.

However, in a SYN flood attack, the attacker never completes the handshake by sending the ACK packet. Additionally, the attacker sends a barrage of SYN packets, leaving the server with multiple half-open connections. The following figure compares a normal TCP handshake with the start of a SYN flood attack.

TCP handshake and SYN flood attack

In some cases, these half-open connections can consume a server’s resources while it is waiting for the third packet, and it can actually crash. More often though, the server limits the number of these half-open connections. Once the limit is reached, the server won’t accept any new connections, blocking connections from legitimate users. For example, Linux systems support an iptables command that can set a threshold for SYN packets, blocking them after the threshold is set. Although this prevents the SYN flood attack from crashing the system, it also denies service to legitimate clients.

Flood Guards

Flood guards use a variety of different methods to protect against SYN flood attacks. Many firewalls and intrusion detection systems include flood guards, which are simply techniques to limit the success of a SYN flood attack. Additionally, some vendors sell flood guard appliances dedicated to detecting and blocking these attacks.

One method of detecting and blocking these attacks is by identifying the source IP address. If a single source IP address is initiating these half-open connections, but never completing them, a flood guard can block all traffic from this IP. However, attackers now commonly spoof the source IP address in each SYN flood packet. Additionally, attackers often launch attacks from multiple systems at the same time, making it difficult to identify legitimate traffic from attacking traffic.

After a comprehensive review by ProCert Labs, the SY0-401 version has been certified as CompTIA Approved Quality Content (CAQC) and covers every aspect of the SY0-401 exam.

It includes the same elements readers raved about in the previous two versions.

Each of the eleven chapters presents topics in an easy to understand manner and includes real-world examples of security principles in action.

You’ll understand the important and relevant security topics for the Security+ exam, without being overloaded with unnecessary details. Additionally, each chapter includes a comprehensive review section to help you focus on what’s important.

Over 400 realistic practice test questions with in-depth explanations will help you test your comprehension and readiness for the exam. The book includes:

A 100 question pre-test

A 100 question post-test

Practice test questions at the end of every chapter.

Each practice test question includes a detailed explanation to help you understand the content and the reasoning behind the question. You’ll be ready to take and pass the exam the first time you take it.

If you plan to pursue any of the advanced security certifications, this guide will also help you lay a solid foundation of security knowledge. Learn this material, and you’ll be a step ahead for other exams. This SY0-401 study guide is for any IT or security professional interested in advancing in their field, and a must read for anyone striving to master the basics of IT security.

Another method is to dynamically adjust the time a system waits for the third packet. For example, the system may normally wait 75 seconds for an ACK after sending the SYN/ACK packet. After sensing a barrage of SYN packets, it can reduce the time it waits for the ACK.

There is a lot more depth to SYN flood attacks and methods used to mitigate them. Additionally, attacks and mitigation techniques continue to evolve. If you’re interested in digging deeper, check out RFC 4987, “TCP SYN Flooding Attacks and Common Mitigations,” here: http://tools.ietf.org/html/rfc4987.

Remember this

A SYN flood attack disrupts the TCP initiation process by withholding the third packet of the TCP three-way handshake. Flood guards protect against SYN flood attacks.

Security+ Practice Test Questions

All questions include explanations so you'll know why the correct answers are correct,

and why the incorrect answers are incorrect.

Pass the Security+ Exam

the First Time You Take It

Multiple quiz formats to let you use these questions based on the way you learn.

Learn mode - randomized. View each of the questions in random order. Learn mode allows you to keep selecting answers until you select the correct answer. Once you select the correct answer, you'll see the explanation. Click here to see how learn mode works.

Learn mode - not randomized. View each of the questions in the same order. Use this if you want to make sure that you see all of the questions. Learn mode allows you to keep selecting answers until you select the correct answer. Once you select the correct answer, you'll see the explanation. Click here to see how learn mode works.

Test mode - randomized. View each of the questions in random order. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.

Test mode - not randomized. View each of the questions in the same order. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.

Test mode - 100 random questions. View 100 random questions from the full test bank similar to how the Security+ exam has a potential maximum of 100 multiple choice questions. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.

Bonus - Performance Based Questions

Additional Security+ questions to help you prepare for the new performance based questions. These are included with the full bank of Security+ practice test questions and are divided into different sections. For example, you'll have access to the following links:

- Performance Based Question - Set 1

You'll see a graphic explaining what you might be required to do on the actual exam to match different types of security to mobile devices and servers in a data center. You'll then have two questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 2

You'll see a graphic explaining what you might be required to do on the actual exam to match different types of attacks with the name of the attack type. You'll then have five questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 3

You'll see a graphic showing a network with computers and servers separated by a firewall. The firewall is used to control traffic between the computers and users using rules within an access control list (ACL). You'll have three questions that test your knowledge and ability to correctly identify the relevant components of the rule. The incorrect answers and explanation provide you with insight into how to correctly answer this type of question on the actual exam.

- Performance Based Question - Set 4

You'll see a graphic explaining what you might be required to do on the actual exam related to what a forensic analyst would do during an investigation. You'll then have two questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 5

You'll see a graphic explaining what you might be required to do on the actual exam to match protocols and ports. You'll then have seven questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 6

You'll see a list of security controls along with a graphic showing devices and locations within an organization, along with instructions on what you might be required to do on the actual exam to match the controls with the devices and locations. You'll then have four questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 7

You'll see a list of authentication methods and authentication factors along with instructions on what you might be required to do on the actual exam to match the authentication methods with the authentication factors. You'll then have six questions that test your knowledge and ability to correctly answer the questions. This set also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 8

You'll see a graphic explaining what you might be required to do on the actual exam to match different types of attacks with the name of the attack type. You'll then have five questions that test your knowledge and ability to correctly answer the questions. This is similar to Set 2 but expands on the possibilities. The set also includes a link to a page showing the end solution for the overall performance based question simulation.

New - Performance Based Question - Set 9

New questions recently added using a different testing engine. See a demo here. This set includes drag and drop and matching questions on ports.

New - Performance Based Question - Set 10

A random set of 20 performance-based questions using drag and drop, matching, sorting, and fill in-the blank. This set includes performance-based questions on RAID.

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